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Megachasma pelagiosMegamouth shark

By Acalia Carter-Martin

Geographic Range

Megamouth sharks (Megachasma pelagios) are found in shallow coastal and open-water pelagic waters. Their range is believed to span the region between latitudes of 40°N and 40°S. These sharks inhabit the Atlantic, Indian, and Pacific oceans. Confirmed sightings or catches include coastal regions of the countries of the United States (Hawaii and San Diego, Catalina Island, San Clemente, California), Australia, Brazil, Indonesia, Japan, the Philippines, Taiwan, Senegal, Vietnam, Sri Lanka, South Africa, Peru, China, and Ecuador. (Acuña-Perales, et al., 2021; Berra and Hutchins, 1990; Castillo-Géniz, et al., 2012; Castro, 2010; Compagno, 1984; Ebert, et al., 2013; Martínez-Ortiz, et al., 2017; Stevens, 1999; Watanabe and Papastamatiou, 2019; White, et al., 2004; Yano, et al., 1999)

Habitat

Megamouth sharks are found in deep, warm oceanic water. Megamouth sharks have been caught at depths of around 600m. These sharks move vertically through the water according to the migration of their prey, which follows the light cycle. Megamouth sharks swim deeper during the day and closer to the surface nocturnally. At night, megamouth sharks are found at depths between 150m and 500m. During the day, megamouth sharks swim at depths between 350m and 600m. Kyne et al. (2019) list the full range of depths from 5m to 1500m below the surface.

Campagno (2002) reported data from one radiotracked shark, finding that in 2 days, it traveled vertically multiple times. At dusk, it was at depths of just 12-25m below the surface, and 120-166m at sunrise. During daylight hours, to moved to 700-850m below the surface. Speeds of travel were 1.5-2.1 km per hour, regardless of time of day. (Castro, 2010; Kyne, et al., 2019; "Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date, Volume 2. Bullhead, Mackerel and Carpet Sharks (Heterodontformes, Lamniformes and Orectolobiformes)", 2002)

  • Range depth
    5 to 1500 m
    16.40 to 4921.26 ft

Physical Description

Megamouth sharks earned their name due to their massive mouth. These sharks have a large terminal mouth and distinct short, round snout. The jaw of megamouth sharks extends past the eyes. The ventral side of megamouth sharks is white, and the dorsal side is grey. Megamouth sharks have dark spots under their lower jaws. Megamouth sharks have a series of small hooked teeth along their top and bottom jaws. Megamouth sharks have two pointed dorsal fins, two tapering pectoral fins, a relatively small pelvic fin, and a small, pointed anal fin.

Male megamouth sharks are typically 425- 515 cm long. Female megamouth sharks are usually above 500 cm long. Female megamouth sharks are larger than males with the largest recorded female measuring 544 cm and 1,040 kg. Another female was reported as "ca. 550 cm" by Nakaya (2001). A juvenile male megamouth shark was caught off the coast of Brazil. It weighed 24.4kg and was 190 cm in length. (Castro, 2010; Ebert, et al., 2013; Nakaya, 2001)

  • Sexual Dimorphism
  • female larger
  • Range mass
    1040 (high) kg
    2290.75 (high) lb
  • Range length
    425 to 550 cm
    167.32 to 216.54 in

Development

The stages of development are not entirely known. No female megamouth sharks with embryos or newborns have been caught. What is known is available is due to by-catches by fishermen and strandings. Female megamouth sharks are not fully mature until they reach about 5m in length. Males megamouth sharks fully mature at about 4 m in length. More specifically, 50% of female megamouth sharks are mature at 5.17 m, and males at 4.26 m. Megamouth sharks are thought to be less than 177 cm at birth. Megamouth sharks are thought to exhibit indeterminate growth, as do all sharks. (Dulvy, et al., 2008; Watanabe and Papastamatiou, 2019)

Reproduction

Little research has found anything conclusive about megamouth sharks' mating systems. However, some female megamouth sharks have been caught with fresh or healing mating scars, and male megamouth sharks have been caught with spermatophores coming from their claspers. The presence of claspers and spermatophores indicates internal fertilization from the males. Mating scars indicate a form of marking or biting of females. (Dulvy, et al., 2008; Kazunari, et al., 1997; Ritter and Amin, 2019; Yano, et al., 1999)

Megamouth sharks are ovoviviparous and show signs of oophagy (eating their own eggs). Fertilization is internal, with males using claspers for fertilization. The number of offspring is unknown. It is believed that megamouth sharks give birth to large offspring in small numbers. Mass at birth and gestation period is unknown. Megamouth sharks are thought to be less than 177 cm at birth. A juvenile caught off the coast of Brazil weighed 24.4kg and was 190cm in length.

It is thought that megamouth sharks mate year-round and give birth near the equator based on the locations that few juveniles have been caught.

Sexual maturity appears to be based on length, as ages are not reported. Female megamouth sharks are not fully mature until they reach about 5m in length. Males megamouth sharks fully mature at about 4 m in length. More specifically, 50% of female megamouth sharks are mature at 5.17 m, and males at 4.26 m. (Dulvy and Reynolds, 1997; Dulvy, et al., 2008; Watanabe and Papastamatiou, 2019)

  • Breeding interval
    Megamouth sharks likely breed year round

The extent of parental investment in megamouth sharks is not known. Being ovoviviparous, the eggs remain in the female while they develop, providing a type of protection until hatching. Males exhibit no parental investment beyond the act of mating. (Dulvy and Reynolds, 1997)

Lifespan/Longevity

The lifespan and longevity of megamouth sharks is unknown due to the lack of sightings. However, basking sharks (Cetorhinus maximus), which researchers believe should belong in the same family as megamouth sharks, have a similar morphology to megamouth sharks and have a lifespan of about 50 years. It is suspected that megamouth sharks have a similar lifespan. These sharks are not kept in captivity. (Compagno, 1984)

Behavior

Megamouth sharks move vertically through the water, being caught at deeper depths during the day, and more shallow depths at night, and are slow, crepuscular swimmers. This behavior likely occurs as megamouth sharks are following the movement of emphasiid shrimps and copepods.

Campagno (2002) reported data from one radiotracked shark, finding that in 2 days, it traveled vertically multiple times. At dusk, it was at depths of just 12-25m below the surface, and 120-166m at sunrise. During daylight hours, to moved to 700-850m below the surface. Speeds of travel were 1.5-2.1 km per hour, regardless of time of day.

Megamouth sharks have also been caught with mating scars and claspers. These indicate internal fertilization by the male. Beyond what is known from strandings and by-catches, not much else is reported about the behavior of these sharks. They are suspected to be solitary, not known to travel in groups. (Acuña-Perales, et al., 2021; Alston, et al., 1986; Castro, 2010; de Moura, et al., 2015; Maisey, 1985; Ritter and Amin, 2019; "Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date, Volume 2. Bullhead, Mackerel and Carpet Sharks (Heterodontformes, Lamniformes and Orectolobiformes)", 2002)

Home Range

Megamouth sharks have no known home range or territory. (Castro, 2010)

Communication and Perception

Not much is known about how megamouth sharks specifically communicate with each other. Like other sharks, megamouth sharks have eyes that include key features found in most vertebrates including the retina, a cornea, and an iris, they also have a tapetum lucidum, which allows them to see in darker waters. As with all sharks, megamouth sharks have both a lateral line and ampullae of Lorenzini. The lateral line aids sharks in recognizing the presence of both predators and prey. The ampulla of Lorenzini uses electrical fields to detect prey.

Megamouth sharks also have a white band on their top jaw. Nakaya (2001) believed it functioned in two ways - as a lure for plankton in low-light conditions, and as a way for conspecifics to recognize one another (because it appears to be unique to megamouth sharks). (Ebert, et al., 2013; Parsons, 2006)

Food Habits

Megamouth sharks are planktotrophic, mostly eating krill. More specifically, megamouth sharks eat shrimp from the family Euphausiidae and copepods. Occasionally, they consume jellyfish, including the species Atolla vanhoeffeni. Stomach contents from a shark in Hawaiian waters found primarily a euphausiid shrimp, Thysanopoda pectinata. In Japan, the shrimp species consumed there was tentatively identified as Euphausia nana..

Megamouths sharks are typically caught in deeper waters in the day and are found closer to the surface at night, following the movements of their prey. During the day, megamouth sharks are caught in oceanic waters at depths around 350m and 600m, at night they are caught around 150m and 500m. (Castro, 2010; Ebert, et al., 2013; "Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date, Volume 2. Bullhead, Mackerel and Carpet Sharks (Heterodontformes, Lamniformes and Orectolobiformes)", 2002)

Predation

The only recorded predator of megamouth sharks is cookiecutter sharks (Isistius brasiliensis). In 1998, three sperm whales (Physeter catodon) were seen attacking a 5-m-long megamouth shark in Indonesian waters. Humans (Homo sapiens) also catch megamouth sharks in occasional bycatch incidents. (Berra and Hutchins, 1990; Honebrink, et al., 2011; "Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date, Volume 2. Bullhead, Mackerel and Carpet Sharks (Heterodontformes, Lamniformes and Orectolobiformes)", 2002; White, et al., 2004)

Ecosystem Roles

Megamouth sharks are planktotrophic, feeding on euphausiid shrimps, jellyfish, and copepods. Predators of megamouth are limited, but may include cookiecutter sharks (Isistius brasiliensis). Parasites of megamouth sharks are pandarid copepods (Dinemolells indeprenslis) and tapeworms. (Castro, 2010; Ebert, et al., 2013; Nagasawa and Senou, 2012; Sawamoto and Matsumoto, 2012)

Commensal/Parasitic Species
  • Copepod (Dinemolells indeprenslis)
  • Tapeworms (Cestoda)

Economic Importance for Humans: Positive

Megamouth shark specimens have been preserved and used for research and educational purposes. They have also been eaten in some countries where they have been caught including Brazil, Taiwan, and the Philippines. (Castro, 2010; Martínez-Ortiz, et al., 2017)

  • Positive Impacts
  • food
  • research and education

Economic Importance for Humans: Negative

Although megamouth sharks are not known to pose any direct threats to humans, they do have the potential to damage or break the fishing nets they are caught in due to their immense size. (Acuña-Perales, et al., 2021; Berra and Hutchins, 1990; Castillo-Géniz, et al., 2012; Castro, 2010; Compagno, 1984; Ebert, et al., 2013; Martínez-Ortiz, et al., 2017; Stevens, 1999; Watanabe and Papastamatiou, 2019; White, et al., 2004; Yano, et al., 1999)

Conservation Status

Megamouth sharks are considered to be a species of "Least Concern" on the IUCN Red List. The US Federal List, CITES, and the State of Michigan List have no special status for megamouth sharks.

Megamouth sharks are typically caught by fisheries in rare bycatch incidents, although they have also been found washed up on shores in Japan and other countries. Many specimens have been caught by fisheries fishing for sharptail mola (Masturus lanceolatus). From 2013-2015, 34 megamouth sharks were caught as bycatch. These sharks, by their rarity, would make overexploitation (intentional or not) a serious threat.

Specimens of megamouth sharks are used for displays, research in education. In U.S. waters in the Pacific Ocean, collection had been prohibited since 2004. As of 2015, it is now legal for fisheries to keep a megamouth specimen if it was caught accidentally - but it must be donated to a museum or for research facilities. In other countries such as Taiwan, megamouth sharks must be reported to the government if caught. Kyne et al. (2019) recommend that if megamouth sharks continue increasing in numbers as bycatch of driftnet fisheries in Taiwan and other Asian fisheries, live release should be required.

All that is known about megamouth sharks is based on 124 records; increasing the sample size without mortality would be a sound step in learning more about the natural history of this shark. (Dulvy, et al., 2014; Kyne, et al., 2019)

Contributors

Acalia Carter-Martin (author), Radford University, Karen Powers (editor), Radford University, Victoria Raulerson (editor), Radford University, Christopher Wozniak (editor), Radford University, Genevieve Barnett (editor), Colorado State University.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

crepuscular

active at dawn and dusk

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

electric

uses electric signals to communicate

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

food

A substance that provides both nutrients and energy to a living thing.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

planktivore

an animal that mainly eats plankton

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

visual

uses sight to communicate

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

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